1. Field
The present disclosure relates to laser-based ophthalmic intervention technologies and, more specifically, to delivering laser energy to create reproducible visible and sub-visible lesions on an eye.
2. Related Art
Every year, thousands of patients in the United States and other countries undergo laser-based interventional treatments of the eye. Such treatments typically involve the application of laser energy in the form of a laser treatment beam having a controlled power and controlled duration to targeted tissue structures to create visible or sub-visible lesions (also referred to herein as “endpoints”). These treatments may be used to address clinical problems, such as diabetic retinopathy, diabetic macular edema, age-related macular degeneration, glaucoma, or the like.
The power and duration required to produce the visible or sub-visible lesions of the desired endpoint may vary from patient to patient due to varying tissue pigmentation. To account for this, clinicians may typically start the treatment by applying a laser treatment beam having a standard power and duration for a particular type of endpoint. Based on the observed endpoint, the clinician may titrate the power and/or duration of the laser treatment beam until a desired endpoint is created. For example, a clinician may apply a laser treatment beam having a particular power and duration in an attempt to produce a barely-visible lesion. However, the laser treatment beam may instead produce a sub-visible lesion. In response, the clinician may increase the power and/or duration by an amount determined by the clinician based on previous experience. The laser treatment beam may again be applied to the patient's eye using the increased power and/or duration settings and the resulting endpoint may be observed. This process may be repeated until a barely-visible lesion is produced.
One inherent drawback to this approach is that there is little uniformity between clinicians in the way they titrate the power and duration of the laser treatment beam due to the subjective nature of visually assessing the lesion grade. Additionally, clinicians often over-adjust the laser treatment beam due to the non-linear relationship between power/duration and the tissue response induced by the laser treatment beam.
Another drawback is that while this technique can be used to produce a desired visible endpoint, the lack of immediate feedback makes this method insufficient for producing sub-visible endpoints. When a sub-visible endpoint is desired, some clinicians titrate to a visible endpoint and then adjust the power and duration of the applied laser pulse using heuristically generated algorithms to achieve their endpoint. Such algorithms generally titrate with continuous wave 50-300 ms (CW) pulses and (1) adjust power by a multiple in the 0.5-2× range, (2) switch to a micropulsed regime (2 ms pulse envelope) with a 5-15% duty cycle, and (3) adjust the overall micropulse burst length (50-2000 ms). These and other titration algorithms are described in J Figueira, J Khan, S Nunes, et al. “Prospective Randomized Controlled Trial Comparing Sub-threshold Micropulse Diode Laser Photocoagulation and Conventional Green Laser for Clinically Significant Diabetic Macular Oedema.” Br J Ophthalmol (2009); 93: 1341-1344, Laursen M L, Moeller F, Sander B, Sjoelie A K. “Subthreshold Micropulse Diode Laser Treatment in Diabetic Macular Oedema.” Br J Ophthalmol 2004; 88:1173-1179, Ohkoshi K, Yamaguchi T. “Subthreshold Micropulse Diode Laser Photocoagulation for Diabetic Macular Edema in Japanese Patients.” Am J Ophthalmol 2010; 149:133-139, Parodi M B, Iacono P, Ravalico G. “Intravitreal Triamcinolone Acetonide Combined with Subthreshold Grid Laser Treatment for Macular Oedema in Branch Retinal Vein Occlusion: A Pilot Study.” Br J Ophthalmol 2008; 92: 1046-1050, and Lavinsky, D., et al. “Randomized Clinical Trial Evaluating mETDRS Versus Normal or High-Density Micropulse Photocoagulation for Diabetic Macular Edema.” Invest Ophthalmol Vis Sci (2011); 52(7): 4314-23. Unfortunately, due to the clinician-to-clinician variation in titration and the non-linear relation ship between power/duration and tissue response, these results are difficult to replicate from one clinician to another.
Thus, a standard and reproducible process for producing visible and sub-visible lesions is desired.